This invention relates to an X-ray CT (computed tomography) apparatus.
In general, an X-ray CT apparatus includes a main detector for detecting an X-ray and its scattered components transmitted through a subject after that X-ray has been emitted from an X-ray source and out-of-plane detectors (OOPS) for detecting scattered components corresponding to the scattered components which have been incident onto the main detector. In this case, accurate X-ray data is evaluated by subtracting the data of the scattered components which have been detected by the OOPS from the detection level of the main detector.
According to the aforementioned method, when the scattered components transmitted through the same subject are incident to the main detector and the OOPS, the measured value a detected by the OOPS and measured value b detected by the main detector are such that the greater part of the measured value b shows an amount of X-ray, m, of a main ray, i.e., a ray directly reaching the main detector after it has been emitted from the X-ray source and transmitted through the subject. In this case, the value e=(b-m) obtained through the subtraction of the amount, m, from the measured value b represents the scattered component. In general, it does not follow that a=e due to the difference, for example, in sensitivity and shape of X-ray detector. It is therefore not always possible to obtain exact X-ray data on the conventional apparatus.